1. Field of the Invention
This invention relates to an adsorption amount sensor for detecting an amount of hydrocarbons and/or an amount of water adsorbed by a zeolite of a hydrocarbon adsorber that adsorbs hydrocarbons or hydrocarbons and water in exhaust gases by using the zeolite as well as a coking sensor for an internal combustion engine, which is employed for detecting an amount of coke deposition (amount of coke or soot deposited) on inner surfaces of a pipe used in the engine.
2. Description of the Prior Art
Generally, in an exhaust system of a gasoline engine or the like, a three-way catalyst is arranged in an intermediate portion of an exhaust pipe in order to purify harmful substances (hydrocarbons, carbon monoxide and nitrogen compounds) in exhaust gases the amount of which can not be reduced sufficiently by engine modifications or EGR (exhaust gas recirculation). The three-way catalyst is heated by exhaust gasses or by using additional means, and activated at temperatures equal to or higher than a predetermined temperature (300xc2x0 C., for instance), thereby purifying harmful substances flowing through the exhaust pipe by oxidation-reduction catalytic actions thereof. However, e.g. when the engine is started in a cold condition, before approximately 30 to 40 seconds have passed after the cold start of the engine, the temperature of the three-way catalyst is lower than the predetermined temperature, and the catalyst remains inactive, so that among the harmful substances, particularly hydrocarbons are emitted from the engine as they are as unburned combustible components. Therefore, in order to prevent emission of hydrocarbons into the air, there has been proposed an engine which incorporates not only the three-way catalyst but also a hydrocarbon adsorber arranged in an exhaust pipe thereof.
This hydrocarbon adsorber includes a zeolite as an adsorbent arranged therein along a direction of flow of exhaust gases. When the exhaust gases are passing through the hydrocarbon adsorber, molecules of hydrocarbons are caused to enter small pores of the zeolite, whereby hydrocarbons are adsorbed by the zeolite. Further, when the zeolite is heated by the exhaust gases to a temperature equal to or higher than a predetermined temperature (e.g. 100 to 250xc2x0 C.), the zeolite desorbs hydrocarbons once adsorbed thereby. The desorbed hydrocarbons are circulated by the EGR and oxidized by the heated three-way catalyst.
As described above, in the hydrocarbon adsorber, although adsorption and desorption of hydrocarbons are repeatedly carried out by the zeolite, the amount of undesorbed hydrocarbons remaining or depositing in the zeolite by a long-term use thereof progressively increases, which results in the degradation of the zeolite, that is, a lowered adsorbing capacity of the zeolite for adsorbing hydrocarbons. If the engine is repeatedly started in such a state, an increasing amount of unadsorbed hydrocarbons is emitted into the air. Therefore, to carry out engine control for desorbing hydrocarbons (e.g. by elevating the temperature of the hydrocarbon adsorber) to cope with the degraded state of the zeolite, or to notify the driver of the degradation of the zeolite, it is required to detect an amount of hydrocarbons adsorbed by the zeolite.
Among methods of detecting the amount of hydrocarbons adsorbed by the zeolite or detecting the degradation of the zeolite, there are a method (1) using a hydrocarbon sensor, a method (2) using temperature sensors, and a method (3) based on measurement of a weight of the zeolite.
According to the method (1) using a hydrocarbon sensor, the hydrocarbon sensor is arranged at a location close to and upstream of a zeolite, and concentrations of hydrocarbons in exhaust gases flowing into the hydrocarbon adsorber are detected to thereby indirectly detect an amount of hydrocarbons adsorbed by the zeolite. According to the method (2) using temperature sensors, as proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-2115, the temperature sensors are arranged at locations upstream and downstream of the zeolite, and an amount of displacement between peaks of temperatures of the respective temperature sensors is detected, thereby detecting the degradation of the zeolite. According to the method (3) based on measurement of a weight of the zeolite, the hydrocarbon adsorber is removed from the exhaust pipe after stopping the engine, and the weight of the hydrocarbon adsorber is directly measured, whereby an amount of hydrocarbons adsorbed by the zeolite is detected based on the difference between the thus measured weight of the hydrocarbon adsorber and a weight of the same before use.
The above methods suffer from the following problems: In the method (1) using the hydrocarbon sensor, an amount of hydrocarbons adsorbed by the zeolite is indirectly detected, so that a detecting error is liable to occur with respect to an actual amount of hydrocarbons adsorbed by the zeolite. Moreover, a hydrocarbon sensor in general use has a limitation of detecting a concentration of a hydrocarbon up to approximately 100 ppm. To obtain a more accurate amount, it is required to provide a high-precision hydrocarbon sensor capable of detecting a concentration of approximately 20 ppm. However, such a high-precision hydrocarbon sensor is expensive, resulting in an increase in manufacturing costs of the whole exhaust system.
Further, in the method (2) using the temperature sensors, not the amount of hydrocarbons adsorbed by the zeolite but the degradation of the zeolite is detected, and hence it is impossible to detect an accurate amount of adsorbed hydrocarbons. In the method (3) based on measurement of a weight of the zeolite, although it is possible to accurately detect an amount of hydrocarbons adsorbed by the zeolite, as described above, it is required to remove the hydrocarbon adsorber from the exhaust pipe when the amount of adsorbed hydrocarbons is detected, which makes the detecting operation troublesome. Moreover, it is impossible to detect an amount of adsorbed hydrocarbons when the engine is in operation.
Depending on the temperature of exhaust gases, the amount of water contained in the exhaust gases is larger than the amount of hydrocarbons contained in the same. The zeolite of the hydrocarbon adsorber usually adsorbs water as well. Therefore, it is possible to detect the degradation of the zeolite by detecting the amount of water adsorbed by the zeolite. However, conventionally, similarly to the method (3), the detection of adsorbed water is carried out by measuring the weight of the zeolite. Hence, the operation for detecting the amount of adsorbed water is troublesome, and moreover it is impossible to detect an amount of adsorbed water when the engine is in operation.
In an internal combustion engine, when fuel is burned, coke or soot of the fuel contained in exhaust gases deposits on the inner wall of the exhaust pipe. When the temperature of the exhaust gases is higher than a predetermined temperature, the coke or soot is burned by the heat of the exhaust gases. However, when the temperature of exhaust gases is low, e.g. immediately after a cold start of the engine, the coke is not burned, and deposits on the inner wall of the exhaust pipe. If the engine is repeatedly started in such a condition, the coke deposits on a three-way catalyst arranged in the exhaust pipe to cause degradation of the performance of the three-way catalyst or increase the flow resistance of the exhaust pipe and the three-way catalyst to exhaust gases. Further, when a hydrocarbon adsorber is arranged in the exhaust pipe, for adsorbing unburned hydrocarbons contained in the exhaust gases, the coke can clog small pores of zeolite of the hydrocarbon adsorber used therein as an adsorbent, to cause degraded performance of the hydrocarbon adsorber. Therefore, to carry out engine control such that the temperature of the hydrocarbon adsorber is elevated to cause the deposited coke to burn, or indirectly determine the degree of degradation of the performance of the device, or further notify the driver of the state of deposition of the coke on the inner wall or inner surfaces of the exhaust pipe, it is required to detect the amount of coke deposition (amount of coke deposited) on the inner wall of the exhaust pipe.
One of conventional methods of detecting the amount of coke deposition is to remove the exhaust pipe from the engine after stopping the engine, and directly measure the weight of the exhaust pipe including the coke, to determine the amount of coke deposition from the difference between the thus measured weight and a weigh of the same before use.
Although this method is capable of accurately detecting the amount of coke deposition, it is required to remove the exhaust pipe from the engine, which is troublesome, and makes it impossible to detect the amount of coke deposition when the engine is in operation.
It is a first object of the invention to provide an adsorption amount sensor which is capable of accurately detecting an amount of hydrocarbons or water adsorbed by a zeolite of a hydrocarbon adsorber, even during operation of an internal combustion engine.
It is a second object of the invention to provide a coking sensor for an internal combustion engine, which is capable of accurately detecting an amount of coke deposition on inner surfaces of a pipe of an internal combustion engine even during operation of the engine.
To attain the first object, according to a first aspect of the invention, there is provided an adsorption amount sensor for detecting an amount of hydrocarbons adsorbed by a zeolite of a hydrocarbon adsorber that adsorbs hydrocarbons in exhaust gases by using the zeolite, the adsorption amount sensor comprising:
a plurality of electrodes arranged in the vicinity
of the hydrocarbon adsorber in a manner opposed to each other and each carrying a zeolite thereon; and
hydrocarbon adsorption amount-detecting means for detecting the amount of hydrocarbons adsorbed, by using a parameter indicative of changes in at least one of a resistance value between the electrodes and an electrical capacitance between the electrodes.
According to this adsorption amount sensor (hereinafter referred to as the xe2x80x9chydrocarbon adsorption amount sensorxe2x80x9d as required), the plurality of electrodes each carrying a zeolite thereon are arranged in the vicinity of the hydrocarbon adsorber having a zeolite for adsorbing hydrocarbons, in a manner opposed to each other, whereby a sensor can be constructed which includes electrodes each carrying thereon a zeolite having the same properties as those of the zeolite of the hydrocarbon adsorber. Hydrocarbons are adsorbed by the zeolites on the electrodes, whereby the resistance value and the electrical capacitance between the electrodes vary with the amount of hydrocarbons adsorbed. This makes it possible to detect the amount of hydrocarbons adsorbed by the zeolite of the hydrocarbon adsorber, by using the parameter indicative of changes in at least one of the resistance value and the electrical capacitance between the electrodes. In other words, since hydrocarbons tend to be adsorbed by the zeolite of the hydrocarbon adsorber and the zeolites on the electrodes substantially in the same manner, the amount of hydrocarbons adsorbed by the zeolites on the electrodes is detected by the hydrocarbon adsorption amount-detecting means, by using the above parameter, whereby the amount of hydrocarbons adsorbed by the zeolite of the hydrocarbon adsorber can be accurately detected or estimated. Further, differently from the conventional method based on a direct measurement of a weight of the zeolite, it is possible to easily detect an amount of hydrocarbons adsorbed by the zeolite and during operation of the engine, without removing the hydrocarbon adsorber from the exhaust pipe.
To attain the first object, according to a second aspect of the invention, there is provided an adsorption amount sensor for detecting an amount of water adsorbed by a zeolite of a hydrocarbon adsorber that adsorbs hydrocarbons and water in exhaust gases by using the zeolite,
the adsorption amount sensor comprising:
a plurality of electrodes arranged in the vicinity of the hydrocarbon adsorber in a manner opposed to each other and each carrying a zeolite thereon; and
water adsorption amount-detecting means for detecting the amount of water adsorbed by the zeolite, by using a parameter indicative of changes in at least one of a resistance value between the electrodes and an electrical capacitance between the electrodes.
According to this adsorption amount sensor (hereinafter referred to as the xe2x80x9cwater adsorption amount sensorxe2x80x9d as required), similarly to the adsorption amount sensor according to the first aspect of the invention, the plurality of electrodes each carrying a zeolite thereon are arranged in the vicinity of the hydrocarbon adsorber having a zeolite for adsorbing hydrocarbons and water, in a manner opposed to each other, whereby a sensor can be constructed which includes electrodes each carrying a zeolite having the same properties as those of the zeolite of the hydrocarbon adsorber. As a result, it becomes possible to detect the amount of water adsorbed by the zeolite of the hydrocarbon adsorber, by using the parameter indicative of changes in at least one of a resistance value and an electrical capacitance between the electrodes. This is because, similarly to the case of the adsorption amount sensor being applied to the hydrocarbon adsorption amount sensor, the resistance value and the electrical capacitance between the electrodes vary with the amount of water adsorbed by the zeolites on the electrodes, and water tends to be adsorbed by the zeolite of the hydrocarbon adsorber and the zeolites on the electrodes substantially in the same manner. Further, degradation of the zeolites can be detected by detecting the amount of water adsorbed by the zeolite of the hydrocarbon adsorber. Still further, it is possible to realize the water adsorption amount sensor as a sensor having the same construction as the hydrocarbon adsorption amount sensor, whereby the adsorption amount sensor can be used both as a hydrocarbon adsorption amount sensor and as a water adsorption amount sensor.
Preferably, the parameter is a voltage generated between the electrodes by application of a predetermined DC voltage between the electrodes.
According to this preferred embodiment of each of the first and second aspects of the invention, the voltage generated between the electrodes by application of the predetermined DC voltage between the electrodes properly reflects changes in the resistance value between the electrodes. Therefore, by using the voltage generated between the electrodes by the application of the predetermined DC voltage as a parameter, it is possible to properly detect the amount of hydrocarbons and/or the amount of water adsorbed by the zeolite of the hydrocarbon adsorber.
Preferably, the adsorption amount sensor further includes an oscillator for outputting a signal having an oscillation frequency dependent on the at least one of the resistance value between the electrodes and the electrical capacitance between the electrodes, and the parameter is the oscillation frequency of the signal.
According to this preferred embodiment of each of the first and second aspects of the invention, the signal output from the oscillator and having an oscillation frequency dependent on the at least one of the resistance value and the electrical capacitance between the electrodes properly reflects changes in the at least one of the resistance value and the electrical capacitance between the electrodes. That is, the oscillation frequency dependent on the resistance value and the electrical capacitance between the electrodes properly reflect changes in the resistance value between the electrodes and the electrical capacitance between the electrodes. Therefore, by using the oscillation frequency of the signal as the parameter, it is possible to properly detect the amount of hydrocarbons and/or the amount of water adsorbed by the zeolite of the hydrocarbon adsorber.
Preferably, the parameter is at least one of a convergence voltage value to which converges a voltage generated between the electrodes by application of a pulse voltage between the electrodes, and a convergence time.
According to this preferred embodiment of each of the first and second aspects of the invention, a voltage generated between the electrodes by the application of a voltage in the form of a pulse (hereinafter referred to as the xe2x80x9cpulse voltagexe2x80x9d throughout the specification and appended claims) between the electrodes converges to a predetermined convergence voltage value, and the convergence voltage value and a convergence time properly reflect the changes in the resistance value and the electrical capacitance between the electrodes. Therefore, by using at least one of the convergence voltage and the convergence time as a parameter, it is possible to properly detect the amount of hydrocarbons and/or the amount of water adsorbed by the zeolite of the hydrocarbon adsorber. It should be noted that throughout the specification and appended claims the term xe2x80x9cconvergence voltage valuexe2x80x9d is used to mean a voltage value to which converges a voltage generated between the electrodes by application of the pulse voltage to the electrodes, while the term xe2x80x9cconvergence timexe2x80x9d is used to mean a rise time required until the voltage generated between the electrodes by the application of the pulse voltage reaches a predetermined proportion of the convergence voltage value.
Preferably, the electrodes have respective portions opposed to each other, the respective portions each having a shape of teeth of a hair comb, and mating with each other in a manner spaced from each other.
In the first aspect of the invention, for instance, the hydrocarbon adsorber is arranged within an exhaust pipe of an internal combustion engine, and the adsorption amount sensor detect the amount of hydrocarbons adsorbed from the exhaust gases from the internal combustion engine by the hydrocarbon adsorber, by using the parameter.
More preferably, the adsorption amount sensor is arranged in the exhaust pipe at a location upstream of the hydrocarbon adsorber.
In the second aspect of the invention, for instance, the hydrocarbon adsorber is arranged within an exhaust pipe of an internal combustion engine, and the adsorption amount sensor detects the amount of water adsorbed from the exhaust gases from the internal combustion engine by the hydrocarbon adsorber, by using the parameter.
More preferably, the adsorption amount sensor is arranged in the exhaust pipe at a location downstream of the hydrocarbon adsorber.
To attain the second object, according to a third aspect of the invention, there is provided a coking sensor for an internal combustion engine having a pipe, the coking sensor detecting an amount of coke deposition on inner surfaces of the pipe,
the coking sensor comprising:
a plurality of electrodes arranged within the pipe in a manner opposed to each other and each having a surface thereof coated with an insulating material; and
coke deposition amount-detecting means for detecting the amount of coke deposition, by using a parameter indicative of changes in at least one of a resistance value between the electrodes and an electrical capacitance between the electrodes.
According to this coking sensor, the plurality of electrodes each coated with an insulating material are arranged within a pipe of the engine in a manner opposed to each other, and coke or soot deposits on the electrodes, whereby the resistance value and the electrical capacitance between the electrodes vary with the amount of coke deposited on the electrodes. This makes it possible to detect the amount of coke deposition within the pipe, by using the parameter indicative of changes in at least one of the resistance value and the electrical capacitance between the electrodes. In other words, since coke or soot tends to deposit on the inner surfaces of the pipe and the electrodes substantially in the same manner, by detecting the amount of coke deposition on the electrodes by using the above parameter, it is possible to accurately detect the amount of coke deposition on the inner surfaces of the pipe. Further, differently from the conventional method which directly measures a weight of the pipe, it is possible to easily detect an amount of coke deposition and even during operation of the engine, without removing the pipe from the engine. Moreover, since the surface of each electrode is coated with the insulating material, it is possible to positively prevent the electrodes from being short-circuited by coke or soot depositing between the electrodes.
Preferably, the parameter is a voltage generated between the electrodes by application of a predetermined DC voltage between the electrodes.
According to this preferred embodiment, the voltage generated between the electrodes by application of the predetermined DC voltage between the electrodes properly reflects changes in the resistance value between the electrodes. Therefore, by using the voltage generated between the electrodes by the application of the predetermined DC voltage as a parameter, it is possible to properly detect the amount of coke deposition on inner surfaces of the pipe.
Preferably, the coking sensor further includes an oscillator for outputting a signal having an oscillation frequency dependent on the at least one of the resistance value between the electrodes and the electrical capacitance between the electrodes, and the parameter is the oscillation frequency of the signal.
According to this preferred embodiment, the signal output from the oscillator and having an oscillation frequency dependent on the at least one of the resistance value and the electrical capacitance between the electrodes properly reflects changes in the at least one of the resistance value and the electrical capacitance between the electrodes. That is, the oscillation frequencies dependent respectively on the resistance value between the electrodes and the electrical capacitance between the electrodes properly reflect changes in the resistance value and the electrical capacitance. Therefore, by using one or both of the oscillation frequencies as a parameter, it is possible to properly detect the amount of coke deposition on the inner surfaces of the pipe.
Preferably, the parameter is at least one of a convergence voltage value to which converges a voltage generated between the electrodes by application of a pulse voltage between the electrodes, and a convergence time.
According to this preferred embodiment, the voltage generated between the electrodes by the application of the pulse voltage between the electrodes converges to a convergence voltage value, and the convergence voltage value and the convergence time properly reflect changes in the resistance value and the electrical capacitance between the electrodes. Therefore, by using at least one of the convergence voltage value and the convergence time as a parameter, it is possible to properly detect the amount of coke deposition on inner surfaces of the pipe.